Each pixel is now represented by a vector P(x,y,z,/) 
where x is column, y line number, z is elevation and I is digital 
count of the pixel. The bird's eye view generation is divided into 
two steps. The first one is to find out a projected vector 
P'(x',y',z') given by azimuth angle, depression angleg , 
distance d between eye position and view plane. The second one 
is to assigned digital count to the newly computed pixel. 
depression angle 
  
image 
X 
  
  
  
  
View plane 
  
Figure 6. Bird's eye view image generation scheme 
The projection is then done by the following formulas: 
x'z xcosq — ysina 
y'=(xsina + ycosa )cos @ + z sin à 
z'=(xsina + ycosa )sin à + zcos à 
  
  
"n Uu d 
=x 
d+z' 
n Uu d 
VS d+z' 
Where 
X .. original column number 
y .. original line number 
z .. original elevation 
x .. transformed column number 
y .. transformed line number 
z ... transformed elevation 
x",y"  ... projected coordinates in view plane 
d .. distance between eye position and view 
plane 
After the position of the pixel in view plane has been 
computed, we must assign to it digital count and to decide 
whether it belongs to hidden surface or not. This will be done by 
simple resampling algorithm applying for the farthest up to the 
nearest line from eye position. 
4. REMOTE SENSING TRAINING ASPECT OF ASEAN 
The primary goal of the ASEAN is training and education. 
All of the functions were designed in a sequence that is 
intuitive and easy to understand. Many Windows control styles 
as graying or disabling menu items were used to prevent 
possible errors, for example, execution of a certain function is 
blocked when the input data is incomplete, or the print menu is 
always grayed when the computing process is not yet finished. 
38 
  
Figure 7. Bird's eye view image display 
The computation algorithms of ASEAN were carefully 
selected and developed to achieve maximal processing speed on 
PC computers and so ASEAN became a real interactive system. 
The Arithmetic Operation menu with capability to input 
arbitrary formula create very interesting module when the user 
can try various formula for image transform. This is very 
flexible approach not only for training but research as well. The 
manual of ASEAN is comprehensive. The help system follows 
Windows style and provides quick searching of guide for 
relevant functions. The most interesting feature of ASEAN that 
is very suitable for training is that most of major functions were 
recorded by Windows Recorder and sample data. Whenever the 
user click Tutorial and select a function, ASEAN will perform 
playback demonstrating visually how to use that function. By 
such an organization the training or self-training become more 
attractive. At the present time, the ASEAN is used for remote 
sensing training in many countries in the SE region and it is 
released through the annual Regional Remote Sensing Seminar 
on Tropical Eco-System Management organized by NASDA, 
UNCRD and ESCAP and other JICA training workshop as 
public domain software. 
  
  
Regional Remote 
Sensing Seminars and 
other 
  
NASDA 
  
  
  
  
  
Education on 
University 
  
  
  
  
  
,  JCA Training 
  
  
  
Rsearch Organization 
ImaSOFT Lab. and Other 
  
  
Figure 8. Development and distribution scheme of ASEAN 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996 
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